Japan began a recess from nuclear-generated electricity, its first in more than four decades, after its sole operating power reactor was halted for scheduled maintenance last night.

Hokkaido Electric Power Co's Tomari No 3 reactor in northern Japan stopped generating electricity yesterday, and fission ceased this morning, said Satoshi Takada, a spokesman for the utility.

Closing the 912-megawatt Tomari unit leaves Japan without an operating power reactor for the first time since May 1970, as plant operators carry out mandatory maintenance or additional safety checks following the Fukushima disaster. The country's 50 nuclear plants provided 30 per cent of its electricity prior to March 11, 2011.

The utilities powering the world's third-biggest economy have been forced to turn to coal, oil and gas-fired plants to keep factories, offices and households supplied with electricity. Buying and importing those fuels is driving up costs and may lead to higher electric bills and a further drag on an economy that's contracted in three of the past four years.

Japan may "momentarily" be without atomic power, the Mainichi newspaper cited Industry Minister Yukio Edano as saying on April 15 after he failed to get agreement from local authorities that reactors at the Ohi plant of Kansai Electric passed safety tests and should resume.

The Ohi atomic plant is located about 95 kilometers (59 miles) northeast of Osaka, the nation's second-biggest metropolitan area. It helps power the Kansai area of western Japan that's about the size of Belgium, has an economy worth $1 trillion -- similar in size to Mexico's -- and is home to the cities of Osaka and Kyoto as well as the factories of Sharp Corp and Panasonic Corp.

Japan's 10 regional power utilities bought record amounts of liquefied natural gas last year to replace nuclear, or 52.9 million metric tons of LNG in the fiscal year ended in March, up 27 per cent from a year earlier, according to data from the Federation of Electric Power Companies.

Use of petroleum, which includes crude and fuel oil, more than doubled to 23.3 million kiloliters (147 million barrels), according to the federation's data. Petroleum consumption was the highest in at least 10 years.

Fuel costs at the nine regional utilities that have atomic plants -- Okinawa Electric Power Co. is the exception -- may more than double to about 7 trillion yen ($87.7 billion) in the year ending March 2013 if reactors remain shut, according to an April 9 report by the industry ministry. Kansai Electric's fuel bills may rise by 800 billion yen to about 1.1 trillion yen, it said.

Kansai Electric's output without nuclear power may be 16.3 per cent short of peak demand this summer if Japan experiences a heat wave similar to the one in 2010, according to the government's April 23 forecast.

The utility would need to turn on half of its 11 reactors to avoid the shortages forecast under the government's worst case scenario, according to Tomoko Murakami, a Tokyo-based nuclear analyst at the Institute of Energy Economics, Japan. Restarting that number of reactors is very unlikely, she said last month.

The Ohi reactors would be the first to come back online since Japan adopted so-called nuclear stress tests or computer simulations to assess each plant's ability to withstand earthquakes, tsunamis and to supply backup power to keep reactor cooling systems running.

Power companies usually take about 10 days to start an idled reactor, according to Tomoe Sugimori, a spokeswoman for Kansai Electric.

The failure of backup power at Tokyo Electric Power Co's Fukushima Dai-Ichi station on March 11 last year caused the worst atomic accident since Chernobyl in 1986, and radiation fallout that forced the evacuation of about 160,000 people.